my most hated character is Garek, hes an intergalatic con man, god he may have a good actor but the character is just an asshole....
I'd have to say quite the opposite. Elim Garak was one of my favorite characters on the show (the other, was The Sisko). The whole thing about Garak, is that you never knew if you could trust him or not, or what stories he told were truthful, and which were blatant lies. He was either a bloodthirsty assassin, or a plain simple tailor. Sometimes a bit of both
Least favorite (by far, in my opinion): Vedek/Kai Winn. She was a b--ch when she was a simple Vedek, and she became moreso after being promoted to Kai. But then, she eventually ended up walking the path of the Pah Wraiths, so it's no surprise there.
2nd runner up, would be Gul Dukat.
(hmm, this post just became very DS9-centric... oh well. Very well-rounded show overall.)